The present invention relates to polycrystalline diamond composite ("PDC") cutters used in drag bits for drilling bore holes in earth formations.
PDC cutters are well known in the art. They have a cemented tungsten carbide body and are typically cylindrical in shape. The cutting surface of the cutter is formed by sintering a PDC layer to a face of the cutter. The diamond layer serves as the cutting surface of the cutter. The cutters are inserted on a drag bit outer body 8 exposing at least a portion of the cutter body 10 and the diamond cutting surface 14 as shown in FIG. 10. Typically, the cutter makes contact with a formation at an angle, i.e., the diamond cutting layer is at an angle to the formation surface. As the bit rotates, the PDC cutting layer edge makes contact and "cuts" away at the formation. At the same time portions of the exposed cutter body also make contact with the formation surface. This contact erodes the cutter body. As the carbide body of the cutter erodes, less and less carbide material is available to support the diamond cutting layer, resulting in the eventual detachment and loss of the PDC cutting layer. Consequently, the cutter is disabled.
Furthermore, as the PDC cutter body erodes, the cutter which is tightly fitted into the bit body loosens and falls out. As the cutting process continues, the fallen cutter can come in contact with or lodge against the remaining cutters causing them to also fail.
Accordingly, there is a need for a cutter with increased resistance to body wear and erosion so as to prevent the detachment of the PDC cutting layer and the consequential "fall-out" of the cutter. There is also a need for a cutter which can still function after the diamond cutting layer is detached. Such a cutter will have an enhanced useful life resulting in less frequent cutter changes and in fewer drilling operation stoppages for replacing failed cutters.